On Sat, Feb 10, 2018 at 02:09:57PM +1030, Alan Modra wrote: > On Fri, Feb 09, 2018 at 08:11:44AM -0600, Segher Boessenkool wrote: > > On Fri, Feb 09, 2018 at 04:12:47PM +1030, Alan Modra wrote: > > > ;; Use r0 to stop regrename twiddling with lr restore insns emitted > > > ;; after the call to __morestack. > > > (define_insn "split_stack_return" > > > - [(unspec_volatile [(use (reg:SI 0))] UNSPECV_SPLIT_STACK_RETURN)] > > > + [(unspec_volatile [(use (reg:SI 0)) (use (reg:SI LR_REGNO))] > > > + UNSPECV_SPLIT_STACK_RETURN)] > > > > I'm not sure what a USE as input of an UNSPEC means -- it should work > > without the USEs? > > Hmm, yes, plain [(reg:SI 0) (reg:SI LR_REGNO)] ought to work. A sniff > test says it's OK but I'll do the whole bootstrap/regtest cycle before > committing. I'm not sure why I put the USE there for r0, probably > because I had the r0 dependency outside the unspec initially then > decided it could replace (const_int 0) inside the unspec vector to > save on useless RTL. I didn't go far enough in trimming the RTL..
For R0 you can use a USE I think, but it should be in a parallel with the unspec then. But LR more appropriately is an input to the unspec, it's not just there to keep the register alive for <some reason>. Having both as inputs works of course. Segher
